An oddball (maybe) cabling question...

sweetbeats

sweetbeats

Reel deep thoughts...
Thinking ahead to the cabling to interface my Ampex MM-1000 and my Soundtracs MX desk...and even further out to when the Ampex is setup for 2" 16-track operation.

The snake from the Ampex to the mixer is a no brainer...I have a 16' 16-channel TRS-TRS snake I made some time ago...the TRS plugs at one end of the snake will be replaced with XLR plugs...Ampex XLR outputs 1~16 to mixer line inputs 17~32...done.

My question is about the cabling to interface the mixer outs to the Ampex. I'm going to be using the Soundtracs' 8 group outputs, but I want each of those group outs to interface with two tape machine inputs (just like you'd do when using something like a Tascam M-300 series mixer to an 8-track...only think 8 groups to 16-tracks instead of 4 groups to 8-tracks).

My crux...I want to just use an 8-channel snake and daisy-chain the connectors at the tape machine rather than use 16-channel snake cable...so what'll happen, for instance, is channel 1 of the snake will go from the mixer group 1 output to the tape machine input 1 and then in series to input 9 (so inside the plug connected to the tape machine input 1 jack will be two sets of 3-conductor cable...the cable coming from the mixer and the cable continuing on up to the plug for input jack 9.

Does that make sense? Any negative issue in doing this?
 
Sounds like it would work fine. As long as you don't need to record like 1 and 9 at the same time. I don't believe the extra cabling will take away from the source.
 
So this like a Y-adapter? I'm not familiar with the switching mechanisms of the tape deck, but I'm guessing the input impedance/load remains the same for both tracks in all operational states, armed or disarmed, or re-routed, or whatever. Should be OK.
 
In any parallel split, the impedance will drop, just like speakers do. So this will mean a harder load for the mixer to drive.

I'd use a patchbay instead and run a proper 16 channel snake to the deck. For switching connections this will be the easiest to work with. Keep in mind this will require more cabling and jacks but its balanced anyway so no biggie if you have the inventory.

Cheers! :)
 
I'm thinking Ghost is spot on about impedance difference. Note the Fostex 80 is setup this way with the inputs to channels 1-4 normalled to 5-8 so you can use it with a 4 buss mixer and not repatch. I'd suggest taking a look at the schematic for that and see how they do it. I have a pdf of the sm, pm me and I can email it to you.

I think you could accomplish this with some kind of buffer/splitter though if you wanted to go the extra work to avoid a patch bay.

Take a look at the Jensen website, I'm assuming you could use some of the same mic splitter technology to make a buffered splitter. Craig Anderton's spluffer would likely work too: (This is in his classic Electronic Projects for Musicians)

https://img530.imageshack.us/img530/4493/splufferji7.gif

Note the IC in that circuit is unavailable, so you can't use his PCB, but there are numerous alternatives. generalguitargadgets has a pcb layout. I don't have EPFM in front of me now, but I think you eliminate the pots for a splitter.

Obviously, you're adding an active or passive stage between the board and the deck by any of these methods, transformer or opamp.
 
So how does Teac/Tascam get away with doing this on so many of their mixers (albeit the split is at the mixer output with the parallel group out jack pairs)?

Also, FYI, at this time it is unbalanced. The Soundtracs MX group outs are unbalanced XLR's as standard. There is a transformer output option which I may build up at some point, but it'll be unbalanced until that time.

Ampex input impedance is 100kohm...Soundtracs output impedance is 50ohm so one split should be fine....shouldn't it? That would still be an impedance ratio of 1000:1 which is plenty AFAIK...
 
The Ghost of FM said:
In any parallel split, the impedance will drop, just like speakers do. So this will mean a harder load for the mixer to drive.---
Click to expand...

If one parallels speakers the resistance will drop not the impedance.

So what Cory may experience here is an increase of resistance which increases the load which may decrease the volumes passed.
 
there should be no impedance issue doing this. But I suspect you will end up recording over a good take at some point.
 
FALKEN said:
there should be no impedance issue doing this.
Click to expand...

This is correct.

Impedance is a factor of an AC current moving through a wire coil in a DC (magnetic) field.

None here unless Cory's magnetic personality affects the issue.
 
Greg...the one-liners...yer still killin' me...:drunk:

Right, yes, I do risk recording over a good take...I'll have to watch my track arming, but it seems to me that there is no reason to add any passive or active stage in between due to the rated impedances and since I'm going to rely on the 8 groups for routing (don't anticipate any regular need to record more than 8 tracks at a time) it certainly seems more simple to use an 8-channel snake rather than a 16...

Somebody stop me if I'm wrong...I ain't buying cheap XLR's for this so I'm gonna save myself the $20 or so as well as the expense of the 16-channel bulk cable if I can without detriment...
 
BTW that input impedance on the Ampex is when operating in an unbalanced mode...that drops to 20kohm when balanced, but that STILL would be an impedance ratio of 200:1 which IIRC is still wayyy above the minimum rule of thumb for that factor...
 
http://www.deltamedia.com/resource/impedance.html

There is a change in impedance, but as Cory pointed out, if both inputs are 100k the parallel impedance will be 50k which is still fine.

Dualing posts here, so 20k balanced would drop to 10k, which is still plenty high for a 50 ohm output. BTW, check out EDCORUSA, a lot of the DIY'ers at prodigypro use these transformers, and a nice 1:1 goes for about $12.
 
Don, the EDCORUSA trannies...that for balancing the outputs on the Soundtracs desk? I'm not transformer savvy...
 
Everything I know I've learned just from the threads at Prodigy-Pro diy. Great place. :cool: Yes, the transformer is to get a true balanced output. (I think you mentioned once that the Ampex also had provision for a transformer balanced input. -- just as an aside, the Otari I have has a transformer balanced input option, and the dbx 180 has a transformer output option, in fact Jensen still lists the transformer --- JT-123DBX, the Dolby 36x series frames have transformer balanced i/o as well.)

The soundtracs info calls for a 1:1 turns ratio and driving a 600 ohm or greater load, so take a look at this:

http://www.edcorusa.com/products/156-xsm600-600.aspx

I know e.g. that people claim good success using Edcors on e.g. the D-AOC or PRR compressors to attain balanced output. They can't be beat for the price, and are wound AFAIK in New Mexico. So you could get a few, try it out and see. The dimensions are almost hte same a couple of mms difference is all, the edcor is about 3mm taller and about 6mm narrower.

Check out the Jensen site as well, there is a ton of information there. I have a few 10k:10k that I (eventually) want to use with the aforementioned compressors ( if I ever get a round tuit.)
 
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I have used a fair amount of Edcor product and have always found it to be very high grade.

They are also very helpful in the support area.
 
Fantastic...thanks fellas. I will have to look into those trannies.

Don, yes, many of the Ampex electronics modules have an octal socket for different plug-in transformers...the 440/MM-1000 models had three options and I have 10 of the matching transformers. My understanding is they sound fine. The 440/MM-1000 electronics have an onboard transformer for the output stage. My understanding of THAT is that it sounds better to bypass it. I'll be trying different output paths to see.
 
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